POV-Ray : Newsgroups : povray.bugreports : Two BBox calculation bugs in CSG and Quadric? : Re: Two BBox calculation bugs in CSG and Quadric? Server Time
28 Sep 2021 18:22:15 EDT (-0400)
  Re: Two BBox calculation bugs in CSG and Quadric?  
From: William F Pokorny
Date: 19 Aug 2019 17:41:17
Message: <5d5b177d$1@news.povray.org>
On 8/19/19 4:28 PM, Andreas Kaiser wrote:
> 
> see CSG::Compute_BBox() in CSG.cpp and Quadric::Compute_BBox(Vector3d&
> ClipMin, Vector3d& ClipMax) in Quadric.cpp:
> ...
>              Make_BBox_from_min_max(BBox, NewMin, NewMax);
>   
>              /* Beware of bounding boxes too large. */
> 
>              if((BBox.size[X] > CRITICAL_LENGTH) ||
>                 (BBox.size[Y] > CRITICAL_LENGTH) ||
>                 (BBox.size[Z] > CRITICAL_LENGTH))
>                  Make_BBox(BBox, -BOUND_HUGE/2, -BOUND_HUGE/2,
> -BOUND_HUGE/2, BOUND_HUGE, BOUND_HUGE, BOUND_HUGE);
> 
> CRITICAL_LENGTH is defined as 1.0e06, BOUND_HUGE/2 as 1.0e10 in both
> cases.
> 
> This code will never shrink/limit the resulting BBox like the comment
> above might suggest.
> It will 'blow up' instead all dimensions of a BBox if just one of its
> dimensions exceeds CRITICAL_LENGTH (which is still smaller than the
> resulting dimension(s)).
>   
> I have no idea what the original intention might have been.
>

That bit of code came in with v3.0, but I have no idea why. I 'think' it 
might be doing what's intended...

The aim isn't to shrink the bounding box, but rather to make it so 
large, if already >1e6 on any side, that it is seen as an infinite 
object and not included in normal bounding. BOUND_HUGE is larger than 
MAX_DISTANCE (1e7). I say this without verifying that this the real 
behavior though.

Bill P.


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